mod_muc_webchat_url: Don't save templated value This prevents changing of other settings without touching the webchat URL from saving the template value. Otherwise the URL will still be advertised when configuring members-only or hidden.

This module blocks configured queries that change server state.

E.g. to make vCard storage read-only:

``` lua
readonly_stores = {
	vcard = { "vcard-temp", "vCard" };
}
```